The determination of directions and angles is required in many areas of use, such as, for example, in geodetic and industrial surveying. Developments in angle measuring technology range via mechanical reading processes to fully automated angle measurement in the prior art today. With automation, higher accuracies of measurement are achievable, observation times can be shortened and measured values can be stored directly and can be further processed in digital form.
Known angle-measuring devices generally comprise a so-called graduated circle and a scanning device. The graduated circle is in the form of a code carrier and has a graduation or coding for position determination on the circle. An apparatus formed for angle determination with graduation or coding is referred to below as code carrier or as graduated circle. The coding is applied to one surface—circle or lateral surface—of the code carrier.
For automatic determination of the angle values, the code carrier rotatable relative to the scanning device around an axis is scanned by means of different techniques. Known scanning methods are electronic-magnetic, electrical and optoelectronic methods. The following embodiments relate to optoelectronic scanning methods and scanning devices.
For determining angle positions from 0° to 360°, the coding is usually arranged in a full circle. The angular resolution of the full circle is determined by the type of coding and by the scanning device used for reading the coding. Thus, the angular resolution is increased, for example, by applying a code in a plurality of tracks or by a finer graduation, the achievable resolution being limited for manufacturing and cost reasons. For example, arrangements of one or more scanning elements on the graduated circle are known for reading the code. CCD line arrays or CCD area arrays may represent, for example, such scanning elements.
Since such scanning devices can in each case scan only a small code region, various methods and apparatuses have been developed for achieving the required accuracies of measurement—which are, for example, in the region of <3 mgon for geodetic applications. Thus, it is in particular usual to combine a coarse measurement with a precise measurement or to achieve the required resolution by interpolation and computational evaluation and to reduce errors of measurement. Angle-measuring apparatuses in this context comprise, for example, additional codings, scanning grids or a plurality of scanners for multiple scanning. However, such known solutions are technically complex and expensive or represent compromises between accuracy of measurement and speed of measurement.